locked
Subject: Networking and the 169.254.x.x. What happens if all 65536 combinations of 169.254.x.x are all in use... RRS feed

  • Question

  • While in a class, I had a question regarding what happens when there are no more available 169.254.x.x APIPA IP Addresses left to choose from.

    When the APIPA is used (due to a DHCP issue), it makes an 169.254.x.x IP address.

    If 169.254.1.1 is in use, it moves on to 169.254.1.2 and if that's in use, it moves on to 169.254.1.3 and so on. What if it gets to the point of trying to use 169.254.255.255. Does the system do something insane, does the system just go round the clock.

    If I had 65536 computers and enough switches on a server, I'd answer the question my self. Does anyone else know the answer to this question?

    Wednesday, August 15, 2018 2:13 PM

Answers

All replies

  • No, I don't know the answer, but I would like to point out that in practice this would be terribly improbable to happen. You would need more that 65 thousand computers connected to the same network segment. But a real network would normally be divided into several segments interconnected by routers. The APIPA addresses only avoid duplicates within the same segment; a different segment separated by a router can repeat the same address. And normally no one segment is so big that it contains 65K machines. Among other things, the amount of traffic generated on the segment by local broadcasts and ARP queries would be horrible. Also, it is likely that the switches would not be able to contain that many addresses in their internal tables. And you would need big switches with lots of ports; you cannot nest two many levels of switches on top of each other because the Ethernet standard limits the number of hops that are allowed between any two endpoints in the network.

    Sunday, August 26, 2018 3:24 PM
  • Off topic for this forum.

    Danny

    Wednesday, October 31, 2018 1:16 PM
    Answerer